Incurred Consolidated Property Casualty Insurance Loss and Loss Expenses on Assumed and Ceded Business (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Net incurred loss and loss expenses	$ 2,524	$ 2,180	$ 2,242
Property, Liability and Casualty Insurance Segment
Direct incurred loss and loss expenses	2,588	2,003	2,135
Assumed incurred loss and loss expenses	24	11	10
Ceded incurred loss and loss expenses	(277)	(4)	(63)
Net incurred loss and loss expenses	$ 2,335	$ 2,010	$ 2,082